关键词： 机械表   电子表   智力游戏   科学知识  

摘要： 电子表的动力是电池中的电能，那么你知道机械表的动力是什么吗？

关键词： Glyoxylate   Mn-III(salen)   electron transfer   kinetics   DFT  

摘要： The kinetics of oxidation of glyoxylic acid (HGl) by Mn-III(salen)(OH ((H(2)salen = N,N'- bis(salicylidene)ethane-1,2-diamine) is investigated at 30.0-45.0A degrees C, 1.83 a parts per thousand currency sign pH a parts per thousand currency sign 6.10, I = 0.3 mol dm(-3)(NaClO4). The products are identified as formic acid, CO2 and Mn-II with the reaction stoichiometry, |Delta[Mn-III]/Delta[HGl]| = 2. The overall reaction involves fast equilibrium pre-association of Mn-III(salen)(OH with HGl and its conjugate base Gl(-) forming the corresponding inner sphere complexes (both HGl and Gl(-) being the monohydrate gem-diol forms) followed by the slow electron transfer steps. In addition, the second order electron transfer reactions involving the inner-sphere complexes and HGl/Gl(-) are also observed. The rate, equilibrium constants and activation parameters for various steps are presented. Mn-III(salen)(OH2)(Gl) is virtually inert to intra molecular electron transfer while the process is facile for Mn-III(salen)(OH2)(HGl)(+) (10(5) k (et) = 2.8 +/- 0.3 s(-1) at 35.0A degrees C) reflecting the involvement of proton coupled electron transfer mechanism in the latter case. A computational study of the structure optimization of the complexes, trans-Mn-III(salen)(OH, trans-Mn-III(salen)(OH2)(Gl), and trans- Mn-III(salen)(OH2)(HGl)(+) (all high spin Mn-III(d(4)) systems), reveals strongest axial distortion for the (aqua)(Gl) complex;HGl bound to Mn (III) centre by the C=O function of the carboxyl group in the (aqua)(HGl) complex facilitates the formation of a hydrogen bond between the proton of the carboxyl group and the coordinated phenoxide moiety ((O-H aEuro broken vertical bar O hydrogen bond distance 1.745 ) and the gem-diols are not involved in H-bonding in either case. A rate comparison for the second order paths: Mn-III(salen)(OH2)(HGl)/Gl)(+/0)+ HGl/Gl(-)-> products, shows that HGl for the (aqua)(HGl) complex is a better reducing agent than Gl(-) for the (aqua)(Gl) compl

关键词： Molecular dynamics   Shape memory alloy   NiAl   Martensite   Phase transformation  

摘要： We use molecular dynamics (MD) with an embedded atom model potential parameterized for NiAl to study martensitic phase transformations in a disordered shape memory alloy. We focus on the role of intrinsic atomic-level variability and mechanical constraints on the martensite and austenite transformation temperatures and on the martensite microstructure for specimens with varying size. We find that periodic system size has a weak effect on transformation temperature all the way to the nanometer scale, with the entropy-stabilized austenite phase slightly penalized with decreasing size. Atomic-level variability in these random alloys leads to significant sample-tosample variability in transformation temperature. The uncertainty in the austenite transformation temperature increases with decreasing size, reaching similar to,10% of the mean value for samples 10 nm on the side. Interestingly, the variability of the high-temperature martensite transition shows little size dependence. We find that a critical size of similar to 40 nm is required to develop multidomain martensite microstructures, and mechanical constraints reduce this critical size to similar to 17 nm, while significantly affecting the transformation temperatures. These results contribute to the understanding of martensitic transformation in nanocrystalline samples and of the fundamental limits of miniaturization of these alloys. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Correlation analysis   Halochromate   Kinetics   Mechanism   Oxidation  

摘要： The oxidation of organic sulfides by imidazolium fluorochromate resulted in the formation of the corresponding sulfoxides. The reaction is first order with respect to imidazolium fluorochromate. A Michaelis-Menten type kinetics was observed with respect to the reactants. The reaction is catalyzed by toluene-p-sulfonic acid. The oxidation was studied in nineteen different organic solvents. An analysis of the solvent effect by Swain's equation showed that the both cation-and anion-solvating powers of the solvents play important roles. The correlation analyses of the rate of oxidation of thirty four sulfides were performed in terms of various single and multiparametric equations. For the aryl methyl sulfides, the best correlation is obtained with Charton's LDR and LDRS equations. The oxidation of alkyl phenyl sulfides exhibited a good correlation in terms of Pavelich-Taft equation. The polar reaction constants are negative indicating an electron-deficient sulfur centre in the rate-determining step. A mechanism involving formation of a sulphenium cation intermediate in the slow step has been proposed.

关键词： Myosins   Lasers   Actins   Cell physiology   Stiffness   Cytoskeleton   Tissue mechanics   Phosphorylation  

摘要： Mechanics has an important role during morphogenesis, both in the generation of forces driving cell shape changes and in determining the effective material properties of cells and tissues. Drosophila dorsal closure has emerged as a reference model system for investigating the interplay between tissue mechanics and cellular activity. During dorsal closure, the amnioserosa generates one of the major forces that drive closure through the apical contraction of its constituent cells. We combined quantitation of live data, genetic and mechanical perturbation and cell biology, to investigate how mechanical properties and contraction rate emerge from cytoskeletal activity. We found that a decrease in Myosin phosphorylation induces a fluidization of amnioserosa cells which become more compliant. Conversely, an increase in Myosin phosphorylation and an increase in actin linear polymerization induce a solidification of cells. Contrary to expectation, these two perturbations have an opposite effect on the strain rate of cells during DC. While an increase in actin polymerization increases the contraction rate of amnioserosa cells, an increase in Myosin phosphorylation gives rise to cells that contract very slowly. The quantification of how the perturbation induced by laser ablation decays throughout the tissue revealed that the tissue in these two mutant backgrounds reacts very differently. We suggest that the differences in the strain rate of cells in situations where Myosin activity or actin polymerization is increased arise from changes in how the contractile forces are transmitted and coordinated across the tissue through ECadherin-mediated adhesion. Altogether, our results show that there is an optimal level of Myosin activity to generate efficient contraction and suggest that the architecture of the actin cytoskeleton and the dynamics of adhesion complexes are important parameters for the emergence of coordinated activity throughout the tissue.

关键词： Vesicles   Lipids   Surface dynamics   Cell membranes   Mechanical properties  

摘要： Multicomponent lipid vesicles are commonly used as a model system for the complex plasma membrane. One phenomenon that is studied using such model systems is phase separation. Vesicles composed of simple lipid mixtures can phase-separate into liquid-ordered and liquid-disordered phases, and since these phases can have different mechanical properties, this separation can lead to changes in the shape of the vesicle. In this work, we investigate the dynamics of phase separation in multicomponent lipid vesicles, using a model that couples composition to mechanical properties such as bending rigidity and spontaneous curvature. The model allows the vesicle surface to deform while conserving surface area and composition. For vesicles initialized as spheres, we study the effects of phase fraction and spontaneous curvature. We additionally initialize two systems with elongated, spheroidal shapes. Dynamic behavior is contrasted in systems where only one phase has a spontaneous curvature similar to the overall vesicle surface curvature and systems where the spontaneous curvatures of both phases are similar to the overall curvature. The bending energy contribution is typically found to slow the dynamics by stabilizing configurations with multiple domains. Such multiple-domain configurations are found more often in vesicles with spheroidal shapes than in nearly spherical vesicles. (C) 2014 AIP Publishing LLC.

关键词： CRYSTALLIZATION -- Kinetics   MELTING   POLYETHYLENE   MATERIALS -- Mechanical properties   HIGH density polyethylene (HDPE)   FOURIER transform infrared spectroscopy  

摘要： Partially melting high-density polyethylene (HDPE) is investigated by differential scanning calorimetry and in situ Fourier transform infrared spectroscopy (FTIR) measurements. The results show that some incompletely molten crystals can be preserved in the partially melting HDPE, thus accelerating subsequent crystallization. Moreover, quantitative calculation of such incompletely molten crystals has been done based on the FTIR results. Interestingly, the kinetically enhanced crystallization results from the improved nucleation rate because of the incompletely molten crystals. Furthermore, such interesting self-nucleation originating from the partially melting HDPE has been deliberately applied to practical polymer processing, i.e., extrusion, aiming to investigate the influence of partially melting HDPE on the microstructural development and the resultant mechanical properties of the extruded products. Unexpectedly, an increment in tensile strength has been achieved in the sheets extruded from partially melting HDPE compared with that extruded from completely melted HDPE. Wide-angle X-ray diffraction and small-angle X-ray scattering results show that the crystallinity, long period, and lamellar thickness increase for the sheets extruded from the partially melting HDPE. These increases are considered to be responsible for the mechanical increment. This work opens a new gateway for applying the self-nucleating effect of partially melting polymer melt into practical processing with the purpose of preparing high-performance polymer products.

关键词： 机械式打捆   压缩机构   多刚体系统   分析仿真  

摘要： 针对目前芦苇等粗纤维造纸原料打包密度低的问题,对机械式高密度打捆压缩机构关键技术进行了研究。基于多刚体系统动力学理论,对机械式打捆压缩机构的压缩机理进行仿真研究,得到工况转速(90r/min)下压缩过程中活塞的运动规律及曲柄铰接处受力变化情况。在进一步研究不同工况转速下曲柄两铰接点最大作用力的变化情况后,提出低速优先的建议。同时,利用有限元方法分析关键零件的应力、应变分布情况,验证其结构设计的合理性。研究结果可为芦苇及其它粗纤维原料高密度打捆压缩提供理论基础,对设备研制提供技术参考。

关键词： 动力学建模   完备性   通用性   时间最优  

摘要： 基于系统动力学模型,针对2点间获取具有最优工作时间负载轨迹问题进行了系统研究。考虑到机械手本身构型特点及动力学模型的完备性与通用性,以多体动力学理论为指导,建立在罗德里格公式定义的系统构件旋转矩阵和Chales定理基础上,采用拉格朗日原理构建系统动力学模型。进而采用线性迭代法(Iterative linear programming,ILP)与系统动力学方程修正相结合的方法,并以一维时间搜索法获取系统最优工作周期。最后针对一3自由度空间机械手进行工作周期优化仿真,并对仿真结果进行分析。

关键词： Fluconazole   Reactive oxygen species   Quantum yields   Photodegradation   By-products   Toxicity  

摘要： The azole fungicide fluconazole has been reported to be persistent in conventional wastewater treatment plants. This study investigated the photodegradation of fluconazole under UV-254 in aqueous solutions. The results revealed that the photodegradation of fluconazole was pH-dependent (2.0-12.0) following the pseudo-first-order kinetics with quantum yield values ranging from 0.023 to 0.090 mol einstein(-1), and it underwent a direct and self-sensitized mechanism involving O-1(2). The main photodegradation by-products were identified and semi-quantitated. The proposed photodegradation pathway included hydroxylative defluorination reaction. The 72 h-NOEC and 72 h-LOEC values for fluconazole using a freshwater unicellular green alga Pseudokirchneriella subcapitata were 10 mu M and 15 mu M. Overall, the photodegradation of fluconazole produced a significant decrease in algal toxicity. It also proved that the photodegradation by-products will not present extra toxicity to this alga than fluconazole itself. (C) 2014 Elsevier Ltd. All rights reserved.